The mouse mutations jp, jpmsd, and qk, which produce defective CNS myelination, will be studied by morphology, morphometry, and tissue culture experimentations. Cultures of normal cerebellum produce abundant myelin; cultures of mutant cerebellum reproduce the specific hypomyelination; and we have now found that for at least one mutant, jpmsd, the hypomyelination in vitro can be reversed by injecting oligodendroglia from normal optic nerve into cultured mutant cerebellum. This glial injection experiment will be refined, standardized, and applied to both cerebellum and optic nerve from all three mutants. Results will be evaluated by quantitation of cultured myelin and SEM and TEM examination of cultures, to observe the behavior of nutant oligodendroglia and axons and determine their precise roles in the mutant diseases. Two of the mutants, jp and jpmsd, will be reexamined on strictly congenic stocks now being developed, to rigorously ascertain whether they are really different. These studies will be extended to other myelin deficient mutants as they are characterized. Two new ones, shi and mld, will definitely become available during this project period.